A hearing aid is generally a one-piece unit that integrates both a microphone and a speaker. The size of the hearing aid must also be small enough to fit into a human ear canal. Due to this size limitation, the performance of the single-piece hearing aid is curtailed by limited power supply. Furthermore, a number of algorithms capable of improving the functionality and performance of the single-piece hearing aid cannot be implemented in any commercial product.
Partly to address these limitations, a two-piece system has been proposed. Generally, a two-piece system includes a first piece, or “ear piece,” having a microphone and a separate second piece, or “pocket piece,” having a processor to process signals. As it is generally larger in size than the earpiece, the pocket piece may provide substantially more power to the entire hearing aid system and allow the implementation of complicated algorithms to process audio signals to enhance the performance of the system.
One such two-piece system has been described in U.S. Pat. No. 5,721,783 (the '783 patent). The '783 patent describes a two-piece hearing aid system comprising an earpiece and a processor unit. The earpiece includes a microphone, a first wireless reflective transponder, a first wireless receiver and a speaker transducer. The processor unit includes a second wireless receiver and a signal processor. According to the '783 patent, sounds from the environment are picked up by the microphone in the earpiece and sent, along with other information, over a two-way wireless link to the processor. The wireless link uses microwaves, and radar technology implements the wireless link to reduce earpiece size and power requirement.
Another exemplary two-piece system is described in U.S. Pat. No. 5,774,791 (the '791 patent). According to the '791 patent, a cordless headset, requiring low power using Time Variant Modulation (TVM) for reception of a magnetic signal is described. The headset area or zone of operations is defined by the magnetic field that the headset operates within and uses a handshake protocol that takes advantage of the TVM fixed clock period. The headset communicates with a base station that includes a TVM transmitter and loop for transmitting a TVM signal to the cordless headset, and an RF or infrared receiver capable of receiving TVM signals from the headset. The base station also incorporates headset protocol logic to control the headset transmission. The headset and base station receiver can both be fixed, mobile or portable and vary with respect to orientation and distance from each other. Both the '783 and '791 patents are incorporated herein by reference.
When the microphone is part of the earpiece, audio signals are first received by the microphone in the earpiece, and then transmitted to the processor in the pocket piece for processing. However, since the microphone also consumes power, the length of time the earpiece may be used without having to replenish the power source is decreased. In addition, the earpiece is subject to movements of a user's head, and therefore the signals received by the earpiece may be distorted and degraded.